add: filter persistence

[pbek]

Summary

Persist the filter state and show unread items by default.

[Grotax]

Hi, maybe I'm too tired but I don't see what this is supposed to do.

I played with this a bit and see no difference in behavior compared to the last alpha.
But that might be related to some cache issue.

So what am I supposed to look for?

[pbek]

It remembers the filter for unread or stared items when you reload the page.

[Grotax]

Ah ok, now I got it to work.

Something I noticed, the filter icon should indicate that a filter is active otherwise I already see the issues that the menu on the left does not work.

[pbek]

Which icon do you mean?
When I reload the page, I have the filter icon reflecting that the filter is active...

[pbek]

@Grotax, do you need some more information for the PR?

[Grotax]

Hi, I mean the filter menu icon.

Otherwise people will forget that they have a filter set when switching into the different categories on the left main menu.
I will add it to the list of things that should be done.

[pbek]

Ok, thank you!